Stability balls in the classroom reflect the research that links physical activity with better learning, says John Kilbourne, a professor of movement science at Grand Valley State University in Allendale, Michigan.

With other research recently surfacing that links sitting to serious health risks, stability balls are also popping up in office spaces nationwide.

Giuliano was inspired to bring the balls into her classroom three years ago after her husband raved of the increased productivity at his office since swapping out chairs for the balls.

The balls are not mandatory in Giuliano's class — only one student has opted for a four-legged chair in the past three years — and strict rules are enforced to prevent injury from horseplay.

Giuliano even bought herself one.

"I don't like sitting on a chair all day...so I started sitting on a yoga ball, and I find I'm more alert," Giuliano tells the Associated Press. "And my message is to try it with your class and see if it works for you."

The chairless-classroom strategy was first used for children with attention problems or autism. Now the balls are popping up in mainstream classes, too.

"It takes away the taboo of wiggling, which most kids do anyway," says Michelle Rowe, executive director of the Kinney Center for Autism at Saint Joseph's University in Philadelphia.

In 2003, a study published in the American Journal of Occupational Therapy concludes that sitting on therapy balls improved behaviour and legible word productivity for students with ADHD.

A Mayo clinic study from 2007 on the benefits of a chairless-classroom finds that the ability to move around while sitting makes students more attentive.

And a 2011 study from the University of Kentucky reveals that teachers prefer having stability balls in the classroom because they are an effective strategy for students with attention-span issues.

"The benefits are greater than I had ever imagined," says Robin Norsworthy, a fifth grade teacher and a participant of a 2012 pilot project in Maine that replaced chairs with stability balls. "The kids are quieter when getting into groups and they move more quickly between tasks. They take great ownership of the stability balls and they love using them."